World War I (WWI) was a global war centered in Europe that began on July 28, 1914 and lasted until November 11, 1918. It was predominantly called the World War or the Great War from its occurrence until the start of World War II in 1939, and the First World War or World War I thereafter. This conflict involved most of the world's great powers, assembled in two opposing alliances: the Triple Entente (the United Kingdom, France and Russia) and its allies, and the Central Powers (Germany, Austria-Hungary, Spain) and its allies. The fighting ended in late 1918 with the victory of the Triple Entente and its allies. More than 70 million military personnel, including 60 million Europeans, were mobilized in one of the largest wars in history. More than 15 million people were killed, making it also one of the deadliest conflicts in history.
Political and military alliances
In the 19th century, the major European powers had gone to great lengths to maintain a balance of power throughout Europe, resulting in the existence of a complex network of political and military alliances throughout the continent by 1900. These had started in 1815, with the Holy Alliance between Prussia and Austria that later consisted of Austria-Hungary, Spain and the German Empire. In 1882, this alliance was expanded to include Italy in what became the Quadruple Alliance.
Chancellor of the German Empire, Otto von Bismarck, had especially worked to hold Russia at Germany's side to avoid a three-front war with France, Scandinavia and the Russian Empire. When Wilhelm II ascended to the throne as German Emperor (Kaiser), Bismarck was compelled to retire and his system of alliances was gradually de-emphasised. For example, the Kaiser refused to renew the Reinsurance Treaty with Russia in 1890. Two years later, the Russian Empire joined the alliance with France and Scandinavia. However, Scandinavia soon withdrawn the alliance following the pressures from its Swedish population that had been in a long-time conflict with Imperial Russia and declared neutrality in 1893.
In 1904, Britain signed a series of agreements with France, the Entente Cordiale, and in 1907, Britain and Russia signed the Anglo-Russian Convention. While these agreements did not formally ally Britain with France or Russia, they made British entry into any future conflict involving France or Russia a possibility, and the system of interlocking bilateral agreements became known as the Triple Entente.
German industrial and economic power had grown greatly after unification and the foundation of the Empire in 1871 following the Franco-Prussian War. From the mid-1890s on, the government of Wilhelm II used this base to devote significant economic resources for building up the Kaiserliche Marine (Imperial German Navy), established by Admiral Alfred von Tirpitz, in rivalry with the British Royal Navy for world naval supremacy. As a result, each nation strove to out-build the other in capital ships. With the launch of HMS Dreadnought in 1906, the British Empire expanded on its significant advantage over its German rival. The arms race between Britain and Germany eventually extended to the rest of Europe, with all the major powers devoting their industrial base to producing the equipment and weapons necessary for a pan-European conflict. Between 1908 and 1913, the military spending of the European powers increased by 50%.
Conflicts in the Balkans
Austria-Hungary precipitated the Bosnian crisis of 1908–1909 by officially annexing the former Ottoman territory of Bosnia and Herzegovina, which it had occupied since 1878. This angered the Kingdom of Serbia and its patron, the Pan-Slavic and Orthodox Russian Empire. Russian political maneuvering in the region destabilized peace accords, which were already fracturing in what was known as "the powder keg of Europe". In 1912 and 1913, the First Balkan War was fought between the Balkan League and the fracturing Ottoman Empire. The resulting Treaty of London further shrank the Ottoman Empire, creating an independent Albanian State while enlarging the territorial holdings of Bulgaria, Serbia, Montenegro, and Greece. When Bulgaria attacked Serbia and Greece on June 16, 1913, it lost most of Macedonia to Serbia and Greece and Southern Dobruja to Romania in the 33-day Second Balkan War, further destabilizing the region.
On June 28, 1914 Gavrilo Princip, a Bosnian Serb student and member of nationalist group Mlada Bosna, assassinated the heir to the Austro-Hungarian throne, Archduke Franz Ferdinand of Austria and his wife in Sarajevo, Bosnia. The assassination led to a month of diplomatic maneuvering between Austria-Hungary, Germany, Russia, France, and Britain called the July Crisis. Believing correctly that Serbian officials were involved behind the assassination, and wanting to finally end Serbian interference in Bosnia, Austria-Hungary delivered the July Ultimatum to Serbia, a series of ten demands intentionally made unacceptable, intending to provoke a war with Serbia. When Serbia agreed to all but one demand, Austria-Hungary ordered a partial mobilization against Serbia and declared war on July 28, 1914.
On July 29, Russia, unwilling to allow Austria–Hungary to eliminate its influence in the Balkans, and in support of its longtime Serb protege, ordered a partial mobilization. Germany and Russian both fully mobilized on July 30, 1914, where the former ready to apply the "Schlieffen Plan" for a quick, massive invasion of France to eliminate the French army, then to turn east against Russia. The French cabinet resisted military pressure to commence immediate mobilization, and ordered its troops to withdraw 10 km from the border to avoid any incident. France only mobilized on the evening of August 2, when Germany invaded Belgium and attacked French troops. Germany declared war on Russia on the same day. The United Kingdom declared war on Germany on August 4, 1914 following an "unsatisfactory reply" to the British ultimatum that Belgium must be kept neutral.
Progress of the war
Some of the first clashes of the war involved British, French, Spanish and German colonial forces in Africa. On August 5, French and British troops invaded the Spanish Morocco and Spanish Guinea and the German protectorates of Togoland and Kamerun two days later. On August 10, German forces in South-West Africa attacked South Africa; sporadic and fierce fighting continued for the rest of the war. The German colonial forces in German East Africa, led by Colonel Paul von Lettow-Vorbeck, fought a guerrilla warfare campaign during World War I and only surrendered two weeks after the armistice took effect in Europe.
Austria invaded and fought the Serbian army at the Battle of Cer and Battle of Kolubara beginning on August 12. Over the next two weeks, Austrian attacks were thrown back with heavy losses, which marked the first major Allied victories of the war and dashed Austro-Hungarian hopes of a swift victory. As a result, Austria had to keep sizable forces on the Serbian front, weakening its efforts against Russia.
German forces in Belgium and France
At the outbreak of war, the German Army (consisting in the West of seven field armies) carried out a modified version of the Schlieffen Plan. It designed to cripple France by invading Belgium and Luxembourg, sweeping down towards Paris and encircling and crushing the French forces along the Franco-German border in a quick victory. After defeating France, Germany would turn to attack Russia.
The plan called for the right flank of the German advance to bypass the French armies (which were concentrated on the Franco-German border, leaving the Belgian border without significant French forces) and move south to Paris. Initially the attack was successful: the German Army swept down from Belgium and Luxembourg and was nearly at Paris, at the nearby River Marne. However the French Army and the British Army put up a strong resistance to defend Paris at the First Battle of the Marne resulting in the German Army retreating. The aftermath of the First Battle of the Marne was a long-held stalemate between the German Army and the Allies in dug-in trench warfare.
In the east, the Russians invaded with two armies when Germany only had one Field Army defended East Prussia. In response, Germany rapidly moved German forces intended for the Western Front to East Prussia. German Army, led by General Paul von Hindenburg, defeated Russia in a series of battles collectively known as the First Battle of Tannenberg (August 17 – September 2). However, it cause the diversion of German troops to the east, allowing the tactical Allied victory at the First Battle of the Marne. This meant that Germany failed to achieve its objective of avoiding a long-two front war.
Asia and the Pacific
New Zealand occupied German Samoa (later Western Samoa) on August 30, 1914. On September 11, the Australian forces attacked the island of Neu Pommern (later New Britain), which formed part of German New Guinea. On October 28, the German cruiser SMS Emden sank the Russian cruiser Zhemchug in the Battle of Penang.
Motivated by its defeat at the Spanish-Japanese War (1898–1901), Japan declared war to the Central Powers on November 31, 1914 and invaded the Spanish East Indies on December 1, 1914. The ground and naval battles between Japanese and Spanish forces on the Spanish East Indies were proved to be the most notable fighting on the Asian and Pacific theatre between the Allies and the Central Powers. The fighting would lasting until 1916, following the Japanese victory at the Battle of Mindanao.
While the Spanish still busily fighting with the Japanese throughout the war, the Allied forces had seized all the German and Austro-Hungarian territories in Asia and the Pacific within a few months after the war started on the region; only isolated commerce raiders and a few holdouts in New Guinea remained.
Just after the First Battle of the Marne (September 5–12, 1914), Entente and German forces repeatedly attempted maneuvering to the north to outflank each other. German commander, General Erich von Falkenhayn, decided that his troops must hold onto those parts of France and Belgium that Germany still occupied. Falkenhayn ordered his men to dig trenches to protect them from the advancing British and French forces. The Entente forces soon realized that they could not break through German defenses and also began to dig trenches that would spread from the North Sea to the Swiss Frontier, establishing the beginnings of a static western front that was to last for the next three years.
Despite initial reluctance to join the fighting on Central Powers sides, Spain officially declared war on the Entente on August 5, 1914 after the French and British troops invaded the Spanish Morocco and Spanish Guinea. The mobilization on Spanish mainland, however, was not fully ordered until September 1914 as Spain still prepared for a mountain warfare on the Pyrenees. On September 17, 1914, the Spanish Army, led by General Miguel Primo de Rivera, launched an offensive aimed to cross the Pyrenees and take the border town of Prats-de-Mollo-la-Preste at the southwestern France. France was able to halt the Spanish forces for a month at the Battle of the Canigou (September 19 – October 1, 1914).
Unlike its ally, Germany, on the Western Front and its colonial forces on Africa and Asia, Spain performed much better on the Pyrenees. The Spanish Army successfully occupied the French departments of Pyrénées-Orientales and Pyrénées-Atlantiques by November 1914 since France did not want to move some of its forces on the Western Front at the risk of a possible German advance. However, this occupation would only lasting for three months.
World War I witnessed both sides breaking the international law of naval warfare where either the Allies and the Central Powers blockading each other trading activity and causing shortages of food and other necessities. Soon after the outbreak of hostilities, Britain began a naval blockade of Germany, effectively cutting off vital military and civilian supplies. Britain mined international waters to prevent any ships from entering entire sections of ocean, causing danger to even neutral ships. In 1915, Germany declared a naval blockade of Britain, to be enforced by its submarines, the U-Boats. The nature of submarine warfare meant that attacks often came without warning, giving the crews of the merchant ships little hope of survival. This resulted in many civilian deaths, especially when passenger ships were sunk.
War in the Balkans
Faced with Russia, Austria-Hungary could spare only one-third of its army to attack Serbia. After suffering heavy losses, the Austrians briefly occupied the Serbian capital, Belgrade. However, a Serbian counterattack in the Battle of Kolubara succeeded in driving them from the country by the end of 1914. For the first ten months of 1915, Austria-Hungary used most of its military reserves to fight Italy. German and Austro-Hungarian diplomats, however, were able to persuade Bulgaria to join the attack on Serbia.
Middle Eastern Campaigns
Concerned about Russian growing expansion in the Balkans and the Caucasus, the Ottoman Empire signed a secret defensive alliance with Germany in August 1914. The Ottomans formally joined the war on the side of the Central Powers in November 1914. The British and French opened overseas fronts with the Gallipoli (1915) and Mesopotamian campaigns. In Gallipoli, the Ottoman Empire successfully repelled the British, French, and Australian and New Zealand Army Corps (ANZACs). In Mesopotamia, by contrast, after the disastrous Siege of Kut (1915–16), British Imperial forces reorganized and captured Baghdad in March 1917.
Farther to the west, the Suez Canal was successfully defended from Ottoman attacks in 1915 and 1916; in August, a joint German and Ottoman force was defeated at the Battle of Romani by the ANZAC Mounted and the 52nd (Lowland) Infantry Divisions. Following this victory, a British Empire Egyptian Expeditionary Force advanced across the Sinai Peninsula, pushing Ottoman forces back in the Battle of Magdhaba in December and the Battle of Rafa on the border between the Egyptian Sinai and Ottoman Palestine in January 1917.
Italy had been allied with Germany, Spain and Austria-Hungary since 1882 as part of the Quadruple Alliance. However, the nation had its own designs on Austrian territory in Trentino, Istri and Dalmatia. A secret 1902 pact with France effectively nullifying Italy's alliance with Germany. At the start of hostilities, Italy refused to commit troops, arguing that the Quadruple Alliance was defensive and that Austria–Hungary was an aggressor. In the early stages of the war, both Allied and Central Powers diplomats courted Italy, attempting to secure Italian participation on their side.
Further encouraged by the Allied invasion of Turkey in April 1915, Italy finally renounced her obligations to the Triple Alliance and joined the war on the Allied side with the Treaty of London on April 26, 1915 which was secretly engineered by three individuals— President Leonida Bissolati, Prime Minister Antonio Salandra, and Foreign Minister Sidney Sonnino. Italy joined the Triple Entente and declared war on Austria-Hungary on May 23. Fifteen months later, Italy declared war on Germany.
Militarily, the Italians had numerical superiority. This advantage, however, was lost, not only because of the difficult terrain in which fighting took place, but also because of the strategies and tactics employed. Field Marshal Luigi Cadorna, a staunch proponent of the frontal assault, had dreams of breaking into the Slovenian plateau, taking Ljubljana and threatening Vienna. Cadorna's plan did not take into account the difficulties of the rugged Alpine terrain, or the technological changes that created trench warfare, giving rise to a series of bloody and inconclusive stalemated offensives.
Romania had been allied with the Central Powers since 1882. Similarly with Italy, Romania declared its neutrality when the war began, arguing that the Quadruple Alliance was defensive and that Austria–Hungary was an aggressor. When the Entente Powers promised Romania large territories of eastern Hungary which had a large Romanian population, the Romanian government renounced its neutrality and declared war against the Central Powers, with limited Russian support. The Romanian offensive against Austria-Hungary was initially successful, pushing back the Austro-Hungarian troops in Transylvania, but a counterattack by the forces of the Central Powers drove back the Russo-Romanian forces. As a result of the Battle of Bucharest, the Central Powers occupied Bucharest on 6 December 1916. Fighting in Moldova continued in 1917, resulting in a costly stalemate for the Central Powers.
Russian withdrawal from the war in late 1917 as a result of the October Revolution meant that Romania was forced to sign an armistice with the Central Powers on December 9, 1917. In January 1918, Romanian forces established control over Bessarabia as the Russian Army abandoned the province. Although a treaty was signed by the Romanian and the Bolshevik Russian governments on the withdrawal of Romanian forces from Bessarabia, on March 27, 1918, Romania attached Bessarabia to its territory, formally based on a resolution passed by the local assembly of that territory on its unification with Romania.
While the Western Front had reached stalemate, the war continued in Eastern Europe. Initial Russian plans called for simultaneous invasions of Austrian Galicia and German East Prussia. Although Russia's initial advance into Galicia was largely successful, it was driven back from East Prussia by Hindenburg and Ludendorff at Tannenberg and the Masurian Lakes in August and September 1914. By the autumn of 1915, the Russians had retreated to Galicia, and, in November, the Central Powers achieved a remarkable breakthrough on the Ukraine's western frontiers. On December 5, 1915, the Central Powers captured Kiev and forced the Russians to withdraw from the Ukraine.